Dual Tank Structure with Integral Secondary Containment

ABSTRACT

A dual tank structure includes first and second tanks with a common secondary containment structure which are all integrally supported on a common base frame. The common base frame includes longitudinal skids so as to be suitable for transport using a conventional winch truck. A passageway with an integral valve therein permits selective communication between the tanks. The common containment structure has a containment volume which is greater than a storage volume of a largest one of the first tank and the second tank and which is less than a combined storage volume of both the first tank and the second tank.

This application claims the benefit under 35 U.S.C. 119(e) of U.S. provisional application Ser. No. 61/684,400, filed Aug. 17, 2012.

FIELD OF THE INVENTION

The present invention relates to a tank structure including first and second tanks and a secondary containment structure all integrally supported on a common skid base for ready transport to and from a hydrocarbon production well, and more particularly the present invention relates to a method of storing produced hydrocarbons including transferring a treated portion of produced hydrocarbons from the first tank to the second tank integrally supported on the common skid base.

BACKGROUND

In the oilfield industry, portable tanks have many uses, including receiving produced fluids from a hydrocarbon well. In this instance, it is known to produce the fluids directly into a first tank on site. Some separation of the initially produced fluids can occur in the first tank such that sand and heavier solids remain in the first tank while lighter hydrocarbons are transferred to a second tank located at the second site also. In this instance, each tank requires secondary containment which is commonly provided by a complex and time consuming assembly of a barrier or dike system about the tanks to support a membrane thereacross upon which the tanks are supported. The containment volumes of the membranes draped over the perimeter barriers are greater than the storage volumes of the tanks.

In some instances, it is known to provide a storage tank in a portable configuration on a skid base as disclosed in U.S. Pat. Nos. 5,392,911 by Gillispie et al. and 4,960,222 by Fields. Each tank requires its own integral containment having a containment volume at least the size of the tank such that the containment portion represents a considerable portion of the material and manufacturing cost of the overall tank structure. In the instance that any treatment is performed on site to separate some of the lighter hydrocarbons, a second tank assembly is required with its own containment structure.

SUMMARY OF THE INVENTION

According to one aspect of the invention there is provided a dual tank structure comprising:

-   -   a base frame which is elongate in a longitudinal direction and         which includes at least two beams extending in the longitudinal         direction along a bottom side so as to be arranged to facilitate         handling and transport of the dual tank structure;     -   a first tank integrally supported on the base frame;     -   a second tank integrally supported on the base frame; and     -   a common containment structure integrally supported on the base         frame and spanning below both the first and second tanks;     -   the common containment structure having a containment volume         which is greater than a storage volume of a largest one of the         first tank and the second tank and which is less than a combined         storage volume of both the first tank and the second tank.

By providing dual tanks with integral containment commonly supported on a single base, a single unit can be delivered to a well site with one truck while providing the function of a first tank for receiving initially produced fluids and a second tank for receiving a second lighter portion of hydrocarbons therein. Also, the containment is only required to exceed the largest of the two tanks by 10% such that when integrally supported with two tanks on a common base, the overall containment volume of the containment structure is permitted to be far less than the combination of the storage volumes of the two tanks. Accordingly, adequate containment for two tanks is provided with minimum manufacturing costs and material costs associated with the containment structure. Even if both tanks are used for common fluid storage, the containment mass and manufacturing costs are considerably reduced as compared to a comparable sized single tank.

Preferably the containment volume is approximately 110% to 120% of the storage volume of the largest one of the first tank and the second tank.

The dual tank structure may be used in combination with a winch truck including a deck and a winch for winching an object onto the deck in which the base frame of the dual tank structure includes an anchor arranged for connection to the winch and the beams of the base frame of the dual tank structure are arranged to be supported on the deck of the winch truck.

The base frame may include a floor panel spanning in the longitudinal direction in which the containment structure comprises a plurality of side walls extending upwardly from the floor panel partway up a height of the first and second tanks to an open top end of the containment volume.

Preferably the first and second tanks are elongate in the longitudinal direction and are mounted on the base frame end to end in series with one another.

There may be provided a continuous cylindrical tank wall supported on the base frame, in which case a divider member is preferably supported in the continuous cylindrical tank wall to define the first tank and the second tank on opposing sides of the divider member within the continuous cylindrical tank wall. The divider member may comprise an assembly of a first wall and a second wall joined to the continuous cylindrical tank wall to define inner ends of the first tank and the second tank respectively.

Preferably there is provided a passageway communicating between the first tank adjacent a top end of the first tank and the second tank. More particularly, there may be provided a riser supported in the first tank having an open top end in communication with an interior of the first tank adjacent the top end of the first tank such that the remaining portion of the passageway communicates between a bottom end of the riser in the first tank and the second tank.

Preferably there is further provided a shut-off valve in series with the passageway including an actuator member supported externally of the first and second tanks for operating the valve between respective open and closed positions.

When a first end of the base frame protrudes longitudinally outward beyond the first and second tanks, there may be provided an enclosure on the base frame between the first end of the base frame and the first tank and a plurality of valves within the enclosure in communication with the first tank. The valves may include a wash valve in communication with a wash line extending into the first tank and supporting wash nozzles thereon and a drain valve in communication with the first tank adjacent the bottom end thereof.

Similarly, when a second end of the base frame protrudes longitudinally outward beyond the first and second tanks, there may be provided an enclosure on the base frame between the second end of the base frame and the second tank and a plurality of valves within the enclosure in communication with the second tank.

There may also be provided a fire tube extending through the first tank or both the first and second tanks in communication between a burner fitting at one end of the fire tube and an exhaust stack at the other end of the fire tube.

The base frame may further comprise a rectangular floor panel spanning horizontally in the longitudinal direction which is supported on the beams which extend along a bottom side of the floor panel such that a plurality of side walls of the secondary containment structure extend upwardly from each side of the floor panel about a full perimeter of the floor panel partway up a height of the first and second tanks to an open top end of the containment volume. In this instance the base frame may yet further comprise a plurality of longitudinally spaced apart tank supports in which each tank support is joined at a bottom side to the floor panel, joined at outer sides to respective side walls of the containment structure, and joined at a top side to the continuous cylindrical tank wall.

According to a second aspect of the present invention there is provided a method of storing produced hydrocarbons from a well, the method comprising:

-   -   providing a dual tank structure comprising:         -   a base frame which is elongate in a longitudinal direction             and which includes at least two beams extending in the             longitudinal direction along a bottom side so as to be             arranged to facilitate handling and transport of the dual             tank structure;         -   a first tank integrally supported on the base frame;         -   a second tank integrally supported on the base frame; and         -   a common containment structure integrally supported on the             base frame and spanning below both the first and second             tanks in which the common containment structure has a             containment volume which is greater than a storage volume of             a largest one of the first tank and the second tank and             which is less than a combined storage volume of both the             first tank and the second tank;     -   directing the produced hydrocarbons directly from the well into         the first tank; and     -   transferring a lighter portion of the produced hydrocarbons from         the first tank to the second tank integrally supported together         on the base frame with the first tank.

The lighter portion of the produced hydrocarbons is preferably drawn from the first tank at a location adjacent a top end of the first tank.

One embodiment of the invention will now be described in conjunction with the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of the dual tank structure.

FIG. 2 is a schematic representation of an end elevational view of the tank structure.

FIG. 3 is a schematic representation of various operating components associated with the tank structure.

FIG. 4 is a side elevational view in partial cross section of the operating components shown in FIG. 3.

In the drawings like characters of reference indicate corresponding parts in the different figures.

DETAILED DESCRIPTION

Referring to the accompanying figures, there is illustrated a dual tank structure generally indicated by reference numeral 10. The tank structure is particularly suited for ready transport to various oilfield sites for storing various fluids therein without the requirement of a secondary containment structure being separately transported and assembled as secondary containment is integrally incorporated into the dual tank structure.

The structure 10 generally comprises a base frame 12 which is elongate in a longitudinal direction between two opposed ends of the structure. The frame includes a floor panel 14 spanning the full length in the longitudinal direction which is generally rectangular to span the full width between two longitudinally extending opposing sides of the structure. The base frame further includes three skid beams 16 spanning longitudinally along the bottom side of the floor panel parallel and spaced apart from one another. The skid beams each comprise a tubular steel member for example having a cross section of 6 inches by 8 inches with suitable spacing between the beams to define a skid base which is compatible with various handling equipment for ready transport, for example for loading onto a winch truck. A cross beam 18 is provided at one or both ends of the skid beams so as to be connected between the skid beams to provide a suitable anchoring point for the winch of a winch truck.

The structure 10 further comprises a first tank 20 and a second tank 22 which are commonly and integrally supported on the base structure by welded connection. The first and second tanks are formed by a common cylindrical tank wall 24 having a longitudinal axis oriented in the longitudinal direction so that the tank wall forms a tank enclosure which is elongate with the base frame. End walls 26 enclose both outer ends of the cylindrical tank wall 24 and a divider member 28 spans perpendicularly to the longitudinal direction across the full cross sectional area of the tank wall at a central location between the two outer ends walls 26 so that the divider member effectively divides the common cylindrical tank wall into the first tank 20 and the second tank 22 on opposing sides thereof. More particularly, the divider member 28 is an assembly of a first wall and a second wall joined about their respective perimeters to the cylindrical wall to define the inner ends 29 of the first tank and the second tank respectively. The first and second walls are separated by a small space which is enclosed by the common cylindrical wall between the walls.

Each resulting tank is also elongate in the longitudinal direction with the first and second tanks being positioned in series end to end abutment relative to one another. The combined length of the tanks is shorter than the overall length of the base frame such that the base frame protrudes longitudinally outward beyond the end wall 26 at the outer end of the corresponding tank wall at both ends of the tank structure. Space is thus provided between the outer end of each tank and the corresponding end of the base frame at both ends of the tank structure to accommodate various valve connections and operating components as described in further detail below.

The common cylindrical tank wall is supported on the base frame by a plurality of longitudinally spaced apart tank supports 30. Each tank support is formed by two panels 32 mounted in a common vertical plane perpendicular to the longitudinal direction to define a common radius upper supporting surface upon which the cylindrical tank wall is engaged and supported. The bottom of the cylindrical tank wall directly engages the upper surface of the floor panel 14 of the base frame to provide support thereto. The two panels 32 of each tank support 30 are laterally spaced apart for engaging opposing sides of the tank wall adjacent the bottom end thereof. Each panel includes a flat bottom edge joined to the upper surface of the floor panel 14 and a curved top edge following the radius of curvature of the tank wall to be engaged in supporting relationship with the tank wall. A generally triangular gap is formed between the innermost edge of each panel and the bottom of the tank wall to provide a port for fluid to be communicated across the tank support along the full length of the containment structure in the longitudinal direction.

A secondary containment structure is also integrally joined to the base frame 12 to span below the first and second tanks along the full width and full length of the tanks. The containment structure comprises four side walls 34 extending upwardly from the four edges of the floor panel to define a continuous perimeter wall extending upward from the perimeter of the floor panel which functions as a bottom wall for the secondary containment structure. The side walls 34 have a height corresponding to less than half the height of the tanks to sufficiently define a containment volume which can contain the full volume of either one of the two storage tanks.

Typically, the first and second storage tanks are arranged to have approximately equal storage volumes. The containment volume of the secondary containment structure is generally arranged to be in the order of 110-120% of the storage volume of the largest tank such that the containment volume is much less than the combined storage volumes of the two tanks together while still meeting the regulations for secondary containment for both tanks individually and collectively when assembled integrally on a common base frame.

To provide additional support to the side walls 34 of the containment structure, the outer most edges of the panels 32 of each tank support are joined to the corresponding longitudinally extending side walls along more than half the height of the wall such that the tank supports also function as gussets to reinforce the side walls of the secondary containment structure.

One or both of the tanks may include the following operating components. Various valves 36 with corresponding fittings communicate through the end wall 26 of the associated tank for loading or unloading fluids from the tank as may be desired. In addition to the loading lines, the tank may include an integral flushing system comprised of one or more wash lines 38 with a respective wash valve communicating through the end wall with the lines extending the length of the tank. Multi-directional nozzles are supported at longitudinal spaced positions along each wash line 38 to be directed at various angles towards a bottom and side walls of the tank for flushing sand and heavier solids from the tank at periodic times desired by the user. A drain line 48 with a corresponding drain valve communicates through the end wall adjacent the bottom end for attaching to a vacuum line to drain wash fluids and debris from the tank during a washing cycle. One or more gauges 42 may also be provided in communication through the end wall for monitoring pressure within the tank.

A suitable enclosure 44 is provided about the operating components and valve connections comprising two laterally opposed side walls spanning longitudinally between the end wall of the tank and the corresponding end of the base frame. A top wall 48 is connected between the top ends of the two side walls 46 to complete the enclosure about the valves and operating components while the outer end at the end of the base frame remains open and unobstructed above the side wall 34 of the secondary containment structure for user access to the operating components. The enclosure 44 and the tanks may be heat insulated. When the enclosure is insulated, a suitable cover member preferably encloses the open end of the enclosure while still permitting ready access thereto. The operating components within the enclosure communicate with the containment volume of the secondary containment structure.

The operating components of each tank may also include a fire tube 50 extending longitudinally through the interior of the tank adjacent the top end thereof in which the fire tube 50 is generally U-shaped between two ends communicating through the common end wall at the outer end of the tank. A burner fitting is provided at one end of the fire tube and an exhaust stack communicates with the other end of the fire tube to provide heating for separating lighter hydrocarbons in at least the first tank.

In use, initially produced fluids can be placed directly into the first tank where some treatment can occur by injection of chemicals or by heating with the fire tube for example. Separated lighter portions of the produced hydrocarbons can then be transferred to the second tank by providing a suitable passageway 52 in communication between the first tank and the second tank.

The passageway includes a first portion defined by a riser tube 54 supported vertically within the first tank. The riser tube 54 includes an open top end in open communication with an interior of the first tank adjacent the top end of the first tank. The bottom end of the riser tube is connected to external piping 56 which defines a second portion of the passageway. The external piping 56 communicates between the bottom end of the riser in the first tank and an open end terminating within the interior of the second tank so as to openly communicate with the second tank adjacent the bottom end thereof.

A shut-off valve 58 is connected in series with the external piping portion of the passageway. The valve 58 includes an actuator member in connection therewith so as to be supported externally of the first and second tanks together with the operating component of the valve for operating the operating component of the valve between respective open and closed positions. The shut-off valve permits fully closing the passageway and maintaining separation between the first and second tanks when desired.

Since various modifications can be made in my invention as herein above described, and many apparently widely different embodiments of same made within the spirit and scope of the claims without department from such spirit and scope, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense. 

1. A dual tank structure comprising: a base frame which is elongate in a longitudinal direction and which includes at least two beams extending in the longitudinal direction along a bottom side so as to be arranged to facilitate handling and transport of the dual tank structure; a first tank integrally supported on the base frame; a second tank integrally supported on the base frame; and a common containment structure integrally supported on the base frame and spanning below both the first and second tanks; the common containment structure having a containment volume which is greater than a storage volume of a largest one of the first tank and the second tank and which is less than a combined storage volume of both the first tank and the second tank.
 2. The dual tank structure according to claim 1 wherein the containment volume is approximately 110% to 120% of the storage volume of the largest one of the first tank and the second tank.
 3. The dual tank structure according to claim 1 in combination with a winch truck including a deck and a winch for winching an object onto the deck and wherein the base frame of the dual tank structure includes an anchor arranged for connection to the winch and wherein the beams of the base frame of the dual tank structure are arranged to be supported on the deck of the winch truck.
 4. The dual tank structure according to claim 1 wherein the base frame includes a floor panel spanning in the longitudinal direction and wherein the containment structure comprises a plurality of side walls extending upwardly from the floor panel partway up a height of the first and second tanks to an open top end of the containment volume.
 5. The dual tank structure according to claim 1 wherein the first and second tanks are elongate in the longitudinal direction and are mounted on the base frame end to end in series with one another.
 6. The dual tank structure according to claim 1 wherein there is provided a continuous cylindrical tank wall supported on the base frame and a divider member supported in the continuous cylindrical tank wall to define the first tank and the second tank on opposing sides of the divider member within the continuous cylindrical tank wall.
 7. The dual tank structure according to claim 6 wherein the divider member comprises an assembly of a first wall and a second wall joined to the continuous cylindrical tank wall to define inner ends of the first tank and the second tank respectively.
 8. The dual tank structure according to claim 1 wherein there is provided a passageway communicating between the first tank and the second tank.
 9. The dual tank structure according to claim 8 wherein the passageway communicates with the first tank adjacent a top end of the first tank.
 10. The dual tank structure according to claim 9 wherein there is provided a riser supported in the first tank having an open top end in communication with an interior of the first tank adjacent the top end of the first tank and wherein the passageway communicates between a bottom end of the riser in the first tank and the second tank.
 11. The dual tank structure according to claim 8 wherein there is provided a shut-off valve in series with the passageway including an actuator member supported externally of the first and second tanks for operating the valve between respective open and closed positions.
 12. The dual tank structure according to claim 1 wherein a first end of the base frame protrudes longitudinally outward beyond the first and second tanks and wherein there is provided an enclosure on the base frame between the first end of the base frame and the first tank and a plurality of valves within the enclosure in communication with the first tank.
 13. The dual tank structure according to claim 12 wherein the valves include a wash valve in communication with a wash line extending into the first tank and supporting wash nozzles thereon and a drain valve in communication with the first tank adjacent the bottom end thereof.
 14. The dual tank structure according to claim 12 wherein a second end of the base frame protrudes longitudinally outward beyond the first and second tanks and wherein there is provided an enclosure on the base frame between the second end of the base frame and the second tank and a plurality of valves within the enclosure in communication with the second tank.
 15. The dual tank structure according to claim 1 wherein there is provided a fire tube extending through the first tank in communication between a burner fitting at one end of the fire tube and an exhaust stack at the other end of the fire tube.
 16. The dual tank structure according claim 1 wherein: a continuous cylindrical tank wall is supported on the base frame and a divider member is supported in the continuous cylindrical tank wall to define the first tank and the second tank on opposing sides of the divider member within the continuous cylindrical tank wall; the base frame further comprises a rectangular floor panel spanning horizontally in the longitudinal direction which is supported on the beams which extend along a bottom side of the floor panel; the containment structure further comprises a plurality of side walls extending upwardly from each side of the floor panel about a full perimeter of the floor panel partway up a height of the first and second tanks to an open top end of the containment volume; and the base frame further comprises a plurality of longitudinally spaced apart tank supports, each tank support being joined at a bottom side to the floor panel, being joined at outer sides to respective side walls of the containment structure, and being joined at a top side to the continuous cylindrical tank wall. 17.-19. (canceled) 